Synthetic fibrous filler and paper containing the filler

ABSTRACT

SYNTHETIC, ORGANIC FILMS, FIBROUS FILLER COMPRISING BLUSHED, FIBROUS POLYSTYRENE HAVING HIGH OPACITY AS REPRESENTED BY SCATTERING COEFFICIENTS OF AT LEAST ABOUT 0.25. THE OPAQUE, FIBROUS POLYSTYRENE IS SUITABLE FOR USE AS FILLER MATERIAL IN THE MANUFACTURE OF PAPER.

United States Paten 3,597,312 SYNTHETIC FIBRUUS FILLER AND PAPERCUNTAININ G THE FILLER Harry F. Kohne, .lr., Glenwood, and Frederick L.Kurrle,

Laurel, Md., and Felipe S. Li, Old Bridge, N..I., assignors to WestvacoCorporation, New York, N.Y. No Drawing. Filed May 7, 1969, Ser. No.822,730 Int. Cl. C03f 45/02; D21h 5/12 US. Cl. 162--146 Claims ABSCT 01?THE DISCLUSURE Synthetic, organic fibrous filler comprising blushed,fibrous polystyrene having high opacity as represented by scatteringcoefiicients of at least about 0.25. The opaque, fibrous polystyrene issuitable for use as filler material in the manufacture of paper.

BRIEF SUMMARY OF THE INVENTION This invention relates to novelcompositions of matter and to their incorporation into paper products.More particularly, it relates to novel and useful synthetic fibrous,white, bright, and opaque filler materials which can be used with or inplace of filler pigments in the production of paper and paperboard.

The trend in the paper industry toward lighter weight printing papershas made it necessary to find a means for maintaining in light weightsheets the optical properties normally found in heavier weight papers.The use of conventional filler pigments, such as clay and titaniumdioxide, in increased amounts to obtain the desired optical properties,results in severe deterioration of strength properties. Opaque, fibrousfillers, such as the blushed cellulose ester fillers described in US.Pat. 3,342,921, provide some opacity without seriously affecting thestrength of the paper. However, the blushed fillers previously known donot approach the opacifying power of TiO and, therefore, more suitablesynthetic fillers have been sought.

The present invention is based upon the discovery that a particularblushed material, radically different from those known in the past, hasan opacity higher than most pigmentary filler materials heretofore knownin the paper industry. We have found that polystyrene, when blushed andin fibrous form, has an extremely high opacity, comparable to TiO asrepresented by its scattering coefficient. This high opacity for blushedpolystyrene fibers is sur prising since the refractive index ofpolystyrene is not particularly high, being about 1.6.

Blushed fibrous polystyrene can readily be incorporated into paper andpaperboard to afford opacity without serious losses in strength. Becausethe new filler is fibrous, it is retained on a paper-forming surface orpapermaking machine to a much greater extent than conventional fillerpigments. Further, since the blushed, fibrous polystyrene has amicroporous structure, it is capable of accepting water and water-basedpaper coatings.

The novel blushed fibrous fillers of this invention can be prepared byan atomizing spray technique wherein a fiber-forining spray solution ofnormally transparent polystyrene is sprayed into a bath containing anon-solvent for the solute portion of the spray solution, thenon-solvent being miscible with the solvent in the polystyrene solution.As the spray formulation is sprayed from the atomizing nozzle, locatedjust above the non-solvent bath, fibrouslike particles are emitted andcollected in the non-solvent bath where the blushing phenomenoncontinues to completion as the solvent in the fibers is diluted anddisplaced by the non-solvent. The fibrous fillers of this invention canalso be made by adding under shear conditions a solution of polystyreneto a non-solvent for polystyrene. Blushed fibers form in thenon-solvent. The final product produced by either technique is a white,very opaque, bright, fibrous polystyrene having a fiber length in therange of about 0.01 mm. to 0.41 mm, a width ranging from about 2.6 to10.5 microns, and a scattering coefiicient up to about 0.61. The blushedfibers have these properties Without any subsequent mechanical sizereduction.

When making blushed, fibrous polystyrene by the spraying techniquedescribed above, distances of about /2 to 4 inches between the atomizingspray nozzle and the bath of non-solvent have been employed, with thepreferred distance being about one inch. Atomizing spray nozzles havingfluid orifice diameters ranging from about 0.028 to 0.100 inch have beenused, with a preferred nozzle diameter of about 0.040 inch. Air issupplied to the spray nozzle at pressures varying from about 50 top.s.i.g.

Many solvents can be used to put polystyrene in solution sufficientlyfor purposes of this invention. For example, the following classes ofsolvents have been used: esters such as ethyl, butyl, isoamyl, carbitol,and methyl cellosolve acetates; ethers, such as dioxane, methylal, andbis (2-ethoxyethylether); ketones, such as methyl ethyl ketone, methylisobutyl ketone, and acetophenone; aromatic hydrocarbons, such astoluene, xylene, Solvesso 100, and Solvesso chlorinated hydrocarbons,such as carbon tetrachloride and ethylene dichloride; mixed solventsystems including mixtures of solvents from above; and mixtures ofsolvents and swelling agents for polystyrene such as one or moresolvents from above mixed with gasoline.

The following non-solvents have been employed in producing the blushed,polystyrene fibers of this invention: water; alcohols, such as methanol,ethanol, and isopropanol; and mixtures of water and alcohol. Also, insome runs, non-solvent has been included in the spray solution, andsolvent has been included in the bath of non-solvent in the same orother runs.

When a stream of polystyrene solution is added to a non-solvent underagitation, the blushed, fibrous product is produced in the non-solvent.When a spray formulation of polystyrene is sprayed according to thisinvention, it is believed that the solution is disrupted by air in theatomizing nozzle and breaks into fiuid filaments as the solution isemitted from the nozzle. Some blushing of the polystyrene fibers occursbefore the fibers reach the nonsolvent due to solvent evaporation, andthe blushing continues in the non-solvent.

Conventional mineral pigments can be included in the polystyrenesolution before the blushed fibers are formed, with the result that theconventional mineral pigments will be encased in the blushed, fibrouspolystyrene. This is one convenient way to pigment the synthetic blushedfibers and to utilize the opacifying abilities of both the blushed,fibrous material and the conventional mineral pigment. The preferredmineral filler for use in this connection is titanium dioxide. Othermineral pigments may be used, such as clay, calcium carbonate, magnesiumoxide, hydrated alumina, and hydrated silica. Depending upon the opacityof the blushed polystyrene fibers, the addition of mineral pigment mayactually decrease the opacity of the final product since the opacity ofthe blushed fibers can be much higher than that of a mineral pigment. Insuch circumstances, the blushed fibers can be utilized as a retentionaid for the mineral pigment.

The scattering coelficient (Kubelka-Munk), an indication of opacifyingpower, of the blushed, fibrous polystyrene of this invention can be ashigh as 0.61, an opacity heretofore unknown for papermaking fillerpigments. A whole range of blushed polystyrene fibrous fillers can beproduced having scattering coefiicients from about 0.25

to about 0.61. The scattering coefficient for conventional filler clayis normally about 0.19, and for TiO about 0.54. Fibrous fillers, knownin the past, have had scattering coefiicients up to about 0.27. Thescattering coefiicients noted above were determined by the methoddescribed subsequently in connection with Examples 1-20.

Various polystyrenes have been used for purposes of producing theblushed fibers of this invention. Molecular weights of the polystyreneshave varied from about 5,000 to about 250,000.

DETAILED DESCRIPTION The invention will be described in greater detailwith the aid of the following examples.

Examples 120 In the following runs, blushed fibrous polystyrene wasproduced in a blender under high shear. In each case, 300 milliliters ofnon-solvent were placed in a Waring blender. With the non-solvent underagitation, 50 grams of a 4 percent solids solution of polystyrene(transparent Dow Styron, general purpose grade, having a molecularweight ranging from 230,000 to 250,000) were metered as a stream intothe non-solvent. The blushed, fibrous polystyrene formed immediatelyupon contact with the non-solvent. In each instance, the resultingblushed product was filtered by use of a Biichner funnel, Washed withnon-solvent and then washed with water, and then incorporated intohand-sheets of paper for appraisal as to light scattering coefiicient(Kubelka-Munk). The solvents in the polystyrene solutions and thenonsolvents used in the blender are set forth below for each run, alongwith the scattering coetficient of the fibrous, blushed polystyrenefiller in each case:

determined at 457 millimicrons by use of an LRL integrating sphererefiectometer. Control handsheets, similar in all respects to the filledsheets except that they contained papermaking pulp only, were alsotested for opacity. By use of Tappi Data Sheet No. 65, which contains agraphical solution of the Kubelka-Munk equations relating Tappi opacity,bulk reflectance, and total light scattering power of the handsheet, thelatter was determined. Total light scattering power is defined as theproduct of the scattering coefficient and the basis Weight of thehandsheet, based on a 3300 square feet ream.

The value for total light scattering power of the Control was divided bythe basis weight of the handsheet to arrive at the scatteringcoefficient of the papermaking pulp. To determine the total scatteringpower for the filler in a filled handsheet, the scattering coefficientfor pulp, determined from the Control, was multiplied by the weight ofpulp in the filled sheet, and this value was subtracted from the totalscattering power of the filled sheet to obtain the total scatteringvalue for the filler portion of the sheet. The scattering coefficientfor the filler was then determined by dividing the total scatteringvalue for the filler by the basis weight of the filler in the handsheet.Scattering coefiicients given throughout this specification weredetermined in the above-described manner.

Examples 2123 In another series of runs, 200 grams of non-solvent wereplaced in a blender and highly agitated. Into the non-solvent weremetered 10 milliliters of a 4 percent solids solution of polystyrene(Dow Styron). The fibrous polystyrene products produced by use of thesolvents and Scattering Solvent Non-solvent coefficient Example No.2

1 Ethyl acetate Methanol 0. 48 2... Butyl acetate ..do.. 0. 48 3...Isoamyl acetate .do. 0. 34 4... Ethyl acetate- Ethanol... 0. 46 5...Carbitol acetate Water. 0. 32 6 0. 31 7 0. 30 8 0. 34 9 0. 34 10.. 0.11-... 0.35 12... Methyl ethyl ketone 0. 13..- Methyl isobutyl ketone..o 0. 49 14.. ..do... 90% methanol, 10% water. 0. 49 15.- do. 70%methanol, 30% water- 0.48 16.. Ol 0. 47 17.. d 0. 28 18.. 80% gasoline,20% toluene do.-. 0.33 19.... gasoline, 40% toluene do. 5 20-.... 40%gasoline, 60% toluene ..do... 6%;

In the above runs, where mixtures of solvents or nonsolvents were used,the percentages noted were by weight.

In the above examples, the fibrous, blushed polystyrene fillers wereincorporated into papermaking furnishes, and handsheets of paper wereprepared in accordance with Tappi Standard T 205 m-5 8, the onlymodification being that the blushed polystyrene fibers were added asfiller to beaten cellulosic papermaking fibers to give filler levels ofapproximately 8% by weight. The screen on the sheet mold on which thehandsheets were formed was 150 mesh, and the consistency of the pulp andfiller furnish was about 0.15%.

In determining the scattering coefficient for each filler, the opacityof the handsheet containing the filler was first measured according toTappi Standard T425 with a B 8: L opacimeter. Reflectance of thehandsheets was non-solvents noted below, were blushed and opaque, asshown by the scattering coefiicients:

Solvesso and are narrow cut aromatic hydrocarbon solvents comprising, byvolume, respectively, 98.9 percent aromatics and 1.1 percent parafiins,and 97 percent aromatics and 3 percent paraffins.

Examples 24-51 As previously discussed, the blushed fibrous products ofthis invention can be produced by an atomizing spray technique wherein asolution of polystyrene is sprayed into a bath of non-solvent for thepolystyrene. In the following examples, approximately 1 liter of varioussolutions of polystyrene (Dow Styron) were sprayed from an air atomizingnozzle, having an internal air mixing chamher and a fluid orifice of0.040 inch, into approximately 20 liters of non-solvent. In some runs,small amounts of non-solvent were included in the spray formulation. Inothers, mixtures of non-solvents were used in the non solvent bath, thepercentages noted below being by weight. Air was supplied to the nozzleat pressures varying from about 80-120 p.s.i.g. The distance between thenozzle and the surface of the non-solvent was about 1 inch, so that thesprayed solution passed through the atmosphere for a short period beforecontacting the nnsolvent. Blushed, fibrous polystyrene was recoveredfrom the bath of nonsolvent by filtering with a Buchner funnel, washingfirst with a 5050 mixture by weight of methanol-water, and then washingwith water. Scattering coeificients were then determined in the mannerpreviously described.

All of the blushed, fibrous polystyrene products of Examples l-54 werebright, white, and opaque and exhibited fiber lengths ranging from about0.01 mm. to 0.41 mm., with diameters ranging from about 2.6 to 10.5microns.

Examples 55-60 In the following runs, conventional mineral pigments wereincluded in polystyrene (Dow Styron) spray formulations. In each case,30 percent of the solids in the spray formulations Was comprised of amineral pigment, and the total solids of the spray formulations wereabout 7 percent. After spraying the formulations into non-solvent,

Percent po ystyrene solids in p y Scattering Solvent solutionNon-solvent coefficient Example No.:

24 Ethyl acetate 11.8 Methanol 0, 2s 25..-. Dioxane 7.0 Water.. 13 26....do 14.0 .....do.. 0. 25 27 Methyl isobutyl ketone (MIB K) 4. 35Methano u. 25 2g 4. 35 70% methanol, 30% wate 0. 34 2 4. 50% methanol,50% Water. 0.42 30.- 4. 35 methanol, 60% water. 0.45 31-. 8. 70 Methanol0, 30 32 8. 70 70% methanol, 30% water- 0.34 33..-. 8. 70 50% methanol,50% water 0. 37 34..-. MIBK 8. 70 40% methanol, 60% water. 0, 41 35....4. 35 90% methanol, 10% MIBK 0, 28 36.... 4. 35 65% methanol, 25% water,10% MIBK. 0.32 37 H 4. 35 methanol, 45% water, 10% MIBK. 0. 61 38,. 4.35 80% methanol, 20% MIBK 0, 30 39 4. 35 60% methanol, 20% Water, 20%MIBK- 0.38 40. 4. 35 methanol, 30% Water, 20% MIBK. 0. 41- 80% gasoline,20% toluene 10. 5 Methanol 0. 33 42. 40% gasoline, toluene-.. 10.5 .do0. 35 43 Xylene. 4. 35 0. 38 44 ..do 8. 0. 40 45..-. xylene, 20%isopropanol. 4. 35 0 44 46..-. Xylene 4. 35 0.43 47.... 80% xylene, 20%isopropanol 4. 35 Q 3 48. Solvesso 150 4.35 0.44 40 80% Solvesso 150,20% isopropano 4. 35 o 0. 45 5 80% Solvesso 150, 20% isopropano 4. 35isopropanol, 10% Solvesso 150.. 0.41 51. Solvesso 4. 35 87% Isopropanol,13% water 0. 42

Examples 52-54 In these runs, polystyrenes having various molecularweights were used in the production of blushed, polystyrene fibers. Thepolystyrene (transparent Borden Styrene the synthetic blushedpolystyrene fibers, pigmented with the mineral fillers, were recoveredand scattering coefficients determined. The blushed polystyrene fibers,encasing mineral pigments, had good optical efficiencies.

Polymer No. 7646) used in Example 52 had a molecular weight of about230,000, the polystyrene (transparent Borden Styrene Polymer No. 8100)used in Example 53 had a molecular weight of about 35,000, and thepolystyrene (transparent Piccolastic D-150) used in Example 54 had amolecular Weight of about 5,000. In each run, 300 grams of non-solventwere placed in a blender and highly agitated. In to the non-solvent weremetered 35 milliliters of a solution of polystyrene prepared bydissolving 8 grams of polystyrene in 200 grams of solvent. The blushedpolystyrene fibers produced were quite opaque as shown by the scatteringcoefiicients in the following table:

As can be seen from above, the blushed polystyrene fibers of thisinvention find great utility in the papermaking field as fillermaterials. They can be used to replace conventional filler pigments orcan be used as retention aids therefor or in conjunction therewith.

While, in the examples above of producing blushed polystyrene fibers bya spraying technique, a one inch spray distance between the atomizingspray nozzle and the surface of the non-solvent has been set forth,distances ranging from about /2 to 4 inches have been used successfullyto produce the blushed fibers. Also, while a fluid nozzle 5 diameter of0.040 inch has been illustrated, diameters ranging from about 0.28 to0.100 have been used.

Various changes may be made in the examples specifically set forth abovewithout departing from the spirit of our invention or the scope of theappended claims.

We claim:

1. A composition of matter comprising synthetic, blushed fibers ofpolystyrene having a microporous structure which is bright, white andopaque, said fibers having lengths ranging from about 0.01 mm. to about0.41 mm. and widths ranging from about 2.6 microns to about 10.5 micronsand produced by preparing a fiber-forming spray solution of polystyrenedissolved in a solvent which is then sprayed from an atomizing nozzleinto a non-solvent bath so that fibers are emitted therefrom andcollected in the non-solvent which is miscible with the solvent wherethe blushing continues to completion as the solvent in the fibers isdiluted and displaced by the non-solvent.

2. The blushed polystyrene fibers of claim 1 characterized as having ascattering coefiicient from about 0.25 to 0.61.

3. The blushed polystyrene fibers according to claim 2 furthercharacterized by the fact that the polystyrene has a molecular weightranging from about 5,000 to about 250,000.

4. The blushed polystyrene fibers according to claim 3 furthercharacterized by the fact that the blushed fibers encase a mineralpigment in the amount of about 30% by weight of said polystyrene fibers.

5. The blushed polystyrene fibers according to claim 4 wherein themineral pigment is selected from the group consisting of clay, calciumcarbonate, hydrated silica, hydrated alumina, titanium dioxide, andmagnesium oxide.

6. Paper comprising cellulosic fibers and synthetic, blushed polystyrenefibers in the amount of approximately 8% by weight of said paper, saidblushed polystyrene fibers being opaque and of microporous structure andhaving lengths ranging from about 0.01 mm. to about 0.41 mm. and widthsranging from about 2.6 microns to about 10.5 microns and produced bypreparing a fiber-forming spray solution of polystyrene dissolved in asolvent which is then sprayed from an atomizing nozzle into anon-solvent bath so that fibers are emitted therefrom and collected inthe non-solvent which is miscible with the solvent where the blushingcontinues to completion as the solvent in the fibers is diluted anddisplaced by the nonsolvent.

7. Paper according to claim 6 wherein the blushed polystyrene fibershave a scattering coefficientfrom about 0.25 to about 0.61.

8. Paper according to claim 7 wherein the polystyrene has a molecularweight ranging from about 5,000 to about 250,000.

9. Paper according to claim 8 further characterized by the fact that thesynthetic, blushed polystyrene fibers encase particles of a mineralpigment in the amount of about 30% by weight of said polystyrene fibers.

10. Paper according to claim 9 wherein the mineral pigment is selectedfrom the group consisting of clay, calcium carbonate, hydrated silica,hydrated alumina, titanium dioxide, and magnesium oxide.

References Cited UNITED STATES PATENTS 2,233,344 2/1941 Helm et al16174X 3,042,970 7/1962 Terenzi 26411 3,099,067 7/ 1963 Merriam et al162-146X 3,215,663 11/196 5 Weisberg 260-4l 3,342,921 9/1967 Brundige etal 26412X 3,354,114 11/1967 Doyle 26041A 3,409,585 PM 1968 Hagemeyer260-41B 3,449,487 6/.1968 Micco et a1. 2=60--41B OTHER REFERENCES 21stAnnual Technical Conference; Technical Papers vol. XI; p. 12; Mar.1-Mar. 4, 1965; Society of Plastics Engineers Inc.

S. LEON BASHORE, Primary Examiner F. FREI, Assistant Examiner US. Cl.X.R.

161174; 162157R, 181A, 181B, 181C, 181D; 260- 41R, 41A, 41B; 26411

